Titanium dioxide in anatase form is known to function as a photocatalyst. When titanium dioxide is exposed to ultraviolet radiation, it produces active species, such as hydroxy radicals, and holes, and breaks apart an organic material. Breaking apart of the organic material produces deodorization and sterilizing effects, and therefore, titanium dioxide is often used in air purification systems.
FIG. 15 illustrates a conventional fluid purification system 31 that has been disclosed, for example, in Japanese Patent Application Laid-open No. H11-276558. The conventional fluid purification system 31 includes a casing 32, and a light source 33 and a photocatalyst structure 34 are arranged inside the casing 32.
The photocatalyst structure 34 surrounds the light source 33. The photocatalyst structure 34 includes a plurality of cylindrical photocatalyst bodies 35 having different diameters. The cylindrical photocatalyst bodies 35 are arranged coaxially at equal intervals and a not shown spacer is arranged between the adjacent cylindrical photocatalyst bodies 35. The cylindrical photocatalyst body 35 is made of a metallic mesh impregnated with a photocatalyst. In this conventional art, the photocatalyst structure 34 is a three-fold structure having three coaxially arranged cylindrical photocatalyst bodies 35.